The present invention relates to a device for transmitting and receiving light from a remote sample. More particularly, the present invention relates to a system for cooling a manifold containing a high energy optical probe used for measuring the optical response of a remote sample to a high energy stimulus.
The ability to monitor particulate matter in process streams and emissions to the air from industrial operations, and particularly the ability to do so in-situ and in real-time, is becoming increasingly important in many industrial processes. This is the case not only because of the desire to control and modify various processes in real-time to improve their efficiency but also to comply with various environmental regulations governing the composition and quantity of various industrial emissions.
In particular, atmospheric emissions of hazardous and/or regulated materials is now strictly controlled by certain state and federal regulatory authorities. Not only are industrial operations required to closely monitor their air emissions but they are also required to do so on a continuous basis. Measurement of concentrations of hazardous materials in stack emissions, however, is a difficult task. Currently, air emissions from industrial operations are measured using extractive sampling followed by off-line chemical analysis, a procedure that is costly and typically having analysis times ranging from days to weeks. Moreover, because certification tests require that more than one sample be taken for a given operating condition the many manual operations involved in extractive sampling introduce a significant potential for sampling error. The long turnaround times inherent in extractive sampling prevent the use of manual air emissions measurements as a realistic method for controlling operating parameters in real-time.
A wide variety of instruments are currently available for on-line analysis of flow streams. However, the optical probes that these instruments use are typically designed for analysis of the concentration of constituents in fluid streams. Furthermore, many of these instruments employ beam dividers or splitters, an arrangement which causes more than 75% of the available light to be lost. Because of the requirement for a second probe that receives light transmitted through the sample, instruments that operate in the transmittance mode are generally unsuited for use in the harsh environments of stack emissions from boilers, incinerators, furnaces and the like.
A method for circumventing many of the problems associated with analysis delays and sampling errors was disclosed in commonly owned U.S. Pat. No. 5,953,120 (herein incorporated by reference). Here, a compact optical probe is provided that is useful for analysis of stack emissions in industrial environments by means of laser spark spectroscopy. The geometry of the prior art optical probe provides a means for making optical measurements in environments where it is difficult and/or expensive to gain access to the vicinity of a flow stream to be measured. However, since this probe is exposed to the environment of the flow stream the optical elements at the probe end inserted into the flow stream suffers from ash fouling. Furthermore, this probe cannot be placed into flow streams where temperatures may exceed more than about a few hundred degrees Fahrenheit.
For the reasons set forth above, it is highly desirable to have an optical probe that permits measurements to be made at a plurality of locations within a flow stream, is rugged enough to be used for monitoring emissions from industrial boilers, incinerators and furnaces and can introduce an optical input of sufficient intensity into the flow stream to heat an entrained particle to a plasma and thus induce an optical response. It is further desired that the probe should be reliable, easy to handle and operate, and robust enough for continuous unmanned operation within a dirty, hostile environment.
The present invention provides an optical probe whereby all of its optical components (source, detector, relay optics, etc.) are either located external to the flow stream being monitored or protected by isolating them from the external stack environment thereby permitting a rugged and robust system. The geometry of the optical probe disclosed herein thus provides a means for making optical measurements in environments where it is difficult and/or expensive to gain access due to the hostile natures of the flow stream, making it particularly useful for remote sampling operations in industrial environments.
The prior art optical probe modified by the present invention comprises a laser spark spectroscopy system for directing a focused incident light beam onto a plurality of analysis locations within a flow stream, creating a spark discharge in the flow stream to ionize any entrained particle or particles, and collecting a return light beam from each of the plurality of analysis locations. The improvement to the optical probe includes a means for shrouding and purging the end of the probe inserted into the flow stream. The optical probe also includes an optical fiber means for receiving light from the return light beam in the vicinity of the final focusing lens.
In one aspect of the present invention, the optical probe includes a cowl or shield at the insertion end of the probe that further includes an orifice, or aperture, through which the incident beam may interact with an effluent flow stream and through which some of the emitted light created by the interaction may be collected. This embodiment is particularly advantageous, because it completely protects sensitive exposed optical surfaces from the contaminating effects of the flow stream ash particulate matter. This embodiment also provides conditions around the insertion end of the probe that do not significantly disturb the surrounding local flow stream environment.
In another aspect of the present invention the shield includes an interior wall that terminates in a conical funnel-section adjacent to the probe aperture.
In still another aspect of the present invention the shield is purged with a dry gas such a dry air or nitrogen.
In another aspect of the present invention the probe aperture is sized to provide only so much clearance as is necessary to permit focusing the laser optics at a point up to several feet beyond the laser source and to permit acquisition of the return light signal by an optical fiber situated at the periphery of the final focusing lens.
In another aspect of the present invention the shield includes a water cooled jacket.
In yet another aspect of the present invention the cooling jacket extends the full length of the probe.